1. Field of the Invention
This invention relates in general to temporary interruption of optical light signals for testing and diagnostics of information-handling data transmission systems, especially fiber optic transmission equipment.
2. Description of the Related Art
The need for increased communications bandwidth is growing rapidly. Internet e-mail traffic volume is increasing exponentially as video, music, voice and image transmission are increasingly carried by internet protocol. The only available technology capable of meeting this demand is dense-wavelength-division-multiplexing (DWDM) fiber optics transmission. Optical network connections are described in layers: the physical layer comprising fiber and optical layers; a logical layer in which the point-to-point connections are established; and a virtual connection layer realized in digital electronics. Historically optical signals were converted to electronic information for switching (routing) in the logical layer, and re-converted to optical signals for re-transmission. Increasingly, switching is being accomplished by physical displacement of mirrors and lenses. AS DWDM becomes dominant it becomes economical to switch traffic by physically re-directing a beam of light rather than by conversion to electronic signals.
The increasing use of fiber optics, and concomitant emphasis on all-optical networks, has resulted in the development of a wide variety of optical switches. Most of these switches divert light beams by means of miniature moving mirrors. These switches range in size and complexity from shutters that simply stop a beam of light to switches that interchange two or more channels, up to large-scale exchanges that handle thousands of incoming fibers and switch any incoming channel to any outgoing channel. Requirements for these switches vary: some must be fast, others must have minimal insertion loss, and physical size for many should be small enough to be placed on a printed circuit board with corresponding electronic components. A diversity of actuation technologies are being prepared to meet these challenges and the resulting business opportunities.
Microelectromechanical systems (MEMS) actuator technology is now receiving funding of sufficient magnitude that the economies of production by large-scale micromachining will be realized. As manufacturing costs are reduced fiber optics systems will compete with telephone, cable, and wireless communication. As this happens, fiber optics will replace electronics and wires because of the enormous bandwidth advantage, leading to all-optical networking. It is reasonable to anticipate that as costs are reduced fiber optics will travel all the way to the desk-top computer.
One criterion for successful transmission is quality of service. Carriers of internet data must provide nearly un-interrupted service as loads vary, equipment fails or undergoes maintenance, and accidents happen. For this reason IP systems are designed with redundancy and a capability for self-diagnostics and automatic re-routing of traffic.
One type of diagnosis requires interrupting an optical path carrying information traffic so that the background noise can be measured. This invention provides an essential component for diagnostics systems in fiber optics: a miniature, PC-board mountable light shutter.
This invention is intended to fill a specific need for a shutter to temporarily block light. The aperture may be as large as several cm long and 2 mm wide, so the shutter must move a significant distance and cover a large area. The timing varies: a shutter may be closed for as little as a few msec or for as much as 500 msec.
The space available for the mechanism is limited: it must be small enough to be placed on a PC board.
It is a general object of the invention to provide a light shutter that has high reliability, robustness, and a long useful lifetime.
Another object is to provide a light shutter of the type described which is electronically driven and is capable of operating at voltages compatible with transistor transistor logic circuitry.